Turbochargers enable the delivery of higher density fuel-air mixtures to one or more combustion chambers or cylinders of an engine in comparison to conventional naturally aspirated engines. An increase in the density of the fuel-air mixture generally improves engine performance and efficiency.
A turbocharger typically includes a turbine wheel and a compressor wheel connected to a common shaft and supported in respective housings (the respective wheels, housings and associated components generally are referred to collectively as the “turbine” and the “compressor”, respectively). The turbine housing includes an exhaust gas inlet and outlet. The inlet couples an exhaust gas conduit of an internal combustion engine to the turbine. The exhaust gas conduit directs exhaust gases from the engine through the turbine housing to rotatably drive the turbine wheel. In turn, the turbine wheel rotatably drives the compressor wheel. The compressor wheel compresses ambient air as the wheel rotates and supplies the resultant compressed charge air through an intake conduit to the engine. In a vehicle application, the exhaust gas outlet of the turbine housing typically is coupled to an exhaust system which may further include pollution and/or noise abatement equipment.
Many turbochargers can deliver charge air from the compressor to the engine at a maximum pressure or boost pressure substantially greater than the engine or the turbocharger can withstand at full load operating conditions. Accordingly, a variety of valves and other pressure control devices have been proposed to limit the maximum boost pressure of the charge air.
Controlled valve arrangements can bleed off a portion of the compressed charge air, or open a bypass flow path around the turbine wheel to reduce the amount of exhaust gases driving the turbine wheel. A wastegate valve, sometimes referred to simply as a “wastegate,” opens and closes to control the flow of exhaust gases through the bypass. Consequently, controlled operation of the wastegate limits the maximum rotational speed of the turbine wheel and the maximum pressure of the charge air supplied to the engine.
Wastegate valve arrangements typically include a control actuator responsive to engine or turbocharger parameters to control opening and closing of the wastegate valve. These control actuators are available in a variety of specific constructions and can be made responsive to any of a selected number or combination of parameters, such as compressor inlet pressure, compressor discharge pressure, turbine inlet pressure or the like.
Some turbochargers include an integral wastegate valve internal to the turbine housing. Turbine designers typically try to optimize the flow of exhaust gases through a turbine housing to maximize the efficiency of the flow of the exhaust gases through the turbine housing to drive the turbine wheel. Forming an integral wastegate valve in the turbine housing introduces further complexity, cost and durability concerns into the design of the turbocharger. Part of the cost increase comes from the need to analyze the effect of the flow of exhaust gases through the bypass when the wastegate valve is open as well as the effect on the flow of exhaust gases when the wastegate is closed. Retrofitting an existing turbocharger to include an internal wastegate generally is impractical or impossible.
Using a remote, external wastegate valve generally improves the performance of a turbocharger that possesses either an integral internal wastegate, an inadequate wastegate or no wastegate at all. Typically, a remote wastegate includes an actuator and either a butterfly valve or a poppet valve to control the flow of exhaust gases. When the remote wastegate valve is opened, exhaust gases from the engine enter the bypass conduit upstream of the turbocharger and exit the system without driving the turbine. Unfortunately, even in the open position these valves remain in the path of the exhaust gas flow and hinder the flow of exhaust gases through the wastegate valve, thus reducing engine efficiency.